Sorry I missed the beginning of this thread and I'm not sure exactly
what model car(b) is in question here but I'll give it a shot:
Peter S. wrote:
> Ok listen up out there! Car still runs a bit rough. (recap - ZS carb
> leaked gas and ran rough - then rebuilt carb and no gas leaks but still runs
> fairly rough. Did the following today:
>
> 1. compression check - All cyl. at 109lbs.
OK
> 2. Ensured timing was correct and operates smoothly. Discovered advance
> vacuum pipe was melted and replaced.
Good
> 3. Attached a vacuum gauge. Reads steadily and changes smoothly.
> Discovered vacuum port for EGR - (top rear section of carb nearest manifold)
> appears to be dead (checked good when carb was on the bench). No vacuum (or
> pressure) measured. I remember wondering which way the carb-to-manifold
> gasket should be since it has a notch. I put it where the old was which was
> pointed to the front of car and downward. THIS CORRECT????????????
There's a gasket and there's a 3/8" spacer here. The important thing is
that the notch aligns with a corresponding hole in the carb flange. The
spacer is not symmetrical, so it's possible for it to be pointed to the
front of the car and downward and still not line up with the hole. I'd
check this.
> 4. Ran engine from new gas in gas can instead of cars gas which may be old.
> 5. pinched off temporarily various vacuum hoses while engine ran to see if
> there was any change. Virtually nil on all of them. Discovered large
> crankcase breather pipes leaking and replaced with new hoses.
This is good. It's important for the crankcase breather hoses to be
leak
free (or will be too lean and impossible to tune). For troubleshooting
purposes, you can just run a single hose from the rocker cover to the
appropriate port on the carb. This bypasses the evaporative lines and
cannisters which could be a source of further vacuum leaks.
> 6. Ensured Choke control operated properly.
Not sure what you did here. ISTR this was a water heated choke?
> 7. Replaced dashpot oil with 3-in-one.
OK
> 8. Used ColorTune. NO color changes when turning idle mixture screw. Can
> see/hear no difference at all despite many turns. Always slightly
> blue/white.
Could be a little lean. Possible vacuum leak. It sounds like you are
turning
the *fine* mixture adjusting screw. This will have little/no effect if
there
are other problems. As Atwell noted; you probably want to adjust the
carb
needle with the "special tool" for more effect.
> 9. Ensured Lucas distributor had gap as specified in manual. Noticed dist.
> shaft seems to move somewhat preventing decent measurement. Cap and rotor
> are new.
Probably OK. A "points type" distributor and water heated choke are
mutually
exclusive wrt to originality. They'll work just fine together, but I
cannot
deduce the model year of the car based on these items.
> 10. HT plug wires all measured 6-10 ohms.
Should be OK
> 11. Plugs cleaned and regapped to 25 thou. Splitfire plugs.
I have no experience with these sparkplugs.
> What am I missing? All of the changes had little or no effect to the
> running of the car though the new vacuum advance pipe does appear to give a
> little more power than before.
Possible vacuum leak(s). Did you check for play in the throttle plate
(butterfly)
shaft bushings when you rebuilt the carb? This is a common source of
air leaks
when the carbs get some age on them. I'd (temporarily) plug the vacuum
port on
the carb. Fit the single hose from rocker cover to car (mentioned
above). Then
check the EGR valve for vacuum leaks with the car at idle. We're not
checking
the control port here (I remember you said this won't hold a vacuum).
We want
to make sure the "business part" of the EGR valve is not leaking air
directly
into the intake manifold. This can be accomplished by spraying carb
cleaner,
WD-40 or other flammable fluid of your choice in and around the EGR
valve.
If this causes the idle to change, then you've probably got a vacuum
leak here.
You can perform the same test on the throttle plate shaft ends to check
4 leaks.
FWIW I'd recommend having a fire extinguisher handy while doing this.
Hope this helps,
Bob
--
Bob & '78 Spitfires
(one of them mine for 21 years)
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